1. Field of the Invention
The present invention relates to a bicycle drive unit and a bicycle chain stay configured and arranged to be coupled to a rear wheel and to be mounted to a bicycle frame.
2. Background Information
A bicycle usually includes a frame, a drive unit, and front and rear wheels that are mounted to front and rear ends of the frame, respectively. The drive unit is mounted to the frame and left and right cranks are rotatably mounted to the drive unit. German Laid-Open Patent Publication No. DE 198 40 576 discloses a drive module as one example of such bicycle drive unit in which a driving device is integrally formed with the rear end of the frame and the drive module is installed in a bicycle. When this type of bicycle drive unit (drive module) is used, the bicycle becomes easier to assemble and the cost of the bicycle can be reduced.
The conventional bicycle drive unit as disclosed in the above mentioned reference includes a support member (one example of a frame main unit and a chain stay) that comprises the rear end of the frame, a crank mounting shaft and a rear wheel axle that are mounted to front and rear end portions of the support member, respectively, right and left cranks that are mounted to both axial ends of the crank mounting shaft, and an internal gear shift hub mounted to the rear wheel axle. The internal gear shift hub includes a brake. A front sprocket is mounted to the right crank, and a rear sprocket is mounted to the internal gear shift hub. A chain that is suspended around both the front and rear sprockets is disposed inside the support member. The support member is movably or swingably mounted to the frame. A cylindrical crank support portion that supports the crank mounting shaft via a pair of bearings protrudes from the front end portion of the support member. The cylindrical crank support portion is supported by the frame in a cantilevered manner.
In the conventional bicycle drive unit described above, because the support member is simply supported by the frame in the cantilevered manner via the crank support portion, it is difficult to maintain the rigidity of the entire drive unit at a high level.
On the other hand, a technology for motorizing gear shifting operations of a gear shift apparatus such as an internal gear shift hub has become widely used in recent years. When such a technology is used, because the support member is supported by the frame in the cantilevered manner in the conventional construction of the bicycle drive unit described above, the space inside the cantilevered support member is small. As a result, it is difficult to mount a gear positioning unit (an example of an electric driving mechanism) having a motor to electrically perform the gear shift operations of the gear shift apparatus or to mount a power supply device for providing electrical power to the gear positioning unit. Consequently, using the above conventional drive unit, it is difficult to accommodate motorization of the gear shift operations of the gear shift apparatus installed in the bicycle.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved bicycle drive unit and bicycle chains stay. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.